I think this is one of those basegame timecrunch issues. The Kamal invasion was in the lore before ESO so it had to stay like that, even if the Underking isn't making any appearance in the official accounts anymore (probably because the Ebonheart Pact wouldn't have been possible with him around).
So the Kamal, despite being different from the Tsaesci, simply couldn't get the attention they deserved at launch. They should not have been describing the Akaviri style as Kamal, that was a bad choice on ZOS' part, but they probably felt it was easier to justify that way.
Rich has shed some insights on the early development in one of this live streams where he was asked what he would do differently if he could travel back in time with the knowledge he has now and his answer was deciding earlier what kind of game they want to make, meaning an elder scrolls game first and MMO second. My intepretation of that and the explanation that followed is that they probably would have paid more attention to the lore in early development, had the One Tamriel changes at launch and designed the zones with that freedom of exploration in mind. My guess is that we would have had more concrete info on the Kamal if that had happened as the Akaviri invasion is a big focus on the Pact's formation story, which I feel got rushed.

Hey when we get akavir as a continent (with many chapters/years worth of content) you will probly get a kamal race and the proper armour/armours to go with.